But now, following last week's election in the United Kingdom, Prime Minister Theresa May's failure to secure an overall majority means that she now faces a number of new battles to fight at home -- before she can even think about dealing with the likes of Barnier and his colleagues in Brussels.

May called the election saying she needed her own strong mandate to deal with other EU leaders. Her disastrous campaign has left her severely weakened, lacking authority at home and abroad. She was described over the weekend by the former Chancellor of the Exchequer George Osborne as a "dead woman walking."

Foreign Secretary Boris Johnson and other leading Brexiteers are insisting there can be no "backsliding" from the government's original Brexit objectives.

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That means leaving the EU Single Market, controlling immigration from the EU and leaving the jurisdiction of the European Court of Justice.

But MPs and ministers who want to retain close ties with the EU say the government will have to compromise to get a deal through the House of Commons.

A key figure in all this is Ruth Davidson, who leads the Scottish Conservative Party. She is a heroine to many in her party after leading a campaign in Scotland which yielded an additional 12 Tory seats and saved the Conservatives from defeat.

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Davidson, who campaigned to remain in the EU, has said it is time to rethink the government's blueprint for Brexit talks to prioritize access to EU markets for UK businesses.

May will also have to get the backing of the Democratic Unionist Party in Northern Ireland for its negotiating position: she will need the backing of its 10 MPs to survive key votes. The DUP does support Brexit, but does not agree with every aspect of the government's approach to date.

The DUP's biggest concern is the border between Northern Ireland and the Irish Republic. At the moment, it is an open border, without barriers or checks, and the DUP want to keep it that way. May has also said there should be no hard border. But the DUP are worried that could be in doubt if the UK left the EU without a deal -- as May has repeatedly said she is willing to do, asserting that "no deal is better than a bad deal."

The minister in charge of the Brexit process, David Davis, has insisted that the government must be prepared to walk away if it cannot get what it wants. He argues that without that option, the government's position would be weakened.

On this the government is also facing opposition from the newly strengthened opposition Labour Party. Its leader, Jeremy Corbyn, who defied expectations and boosted his party's standing, has said it would be an "economic disaster" to leave the EU without agreement. Any final Brexit arrangement will be put to Parliament and both Labour and the Scottish Nationalists will use every opportunity to push their agenda for a close trading relationship with the EU and a deal which protects jobs and workers' rights.

Leaving the European Union will require up to a dozen new laws, covering issues such as immigration rules, customs arrangements, sovereignty and workers' rights. There will be a Great Repeal Bill, bringing all EU legislation affecting the UK back to Britain.

The opposition parties are ready to oppose every proposal they don't like. Without a majority in the House of Commons, the government will struggle to get its way. A rebellion by just a handful of Conservative MPs will result in defeat for the government.

The Brexit workload will leave little time for other parliamentary business.

Some MPs are arguing for a cross-party commission or committee to try to achieve consensus on the way ahead. Ministers are already conceding they may have to prune back their ambitions.

The clock is already ticking: Britain will leave the EU in the spring of 2019 unless it can get agreement with the rest of the EU for an extension to the timetable.

May spent months telling us that "Brexit means Brexit." It will also mean battle after battle -- not just with 27 other EU nations, but with her parliamentary opponents and her own disgruntled party.